European Patent EP 0 941 470 describes a fluorescence correlation spectroscopy module for a microscope. The FCS module can additionally be connected to a microscope of any desired design. Fluorescence correlation spectroscopy allows the investigation of molecular dynamic processes to be studied. For this purpose, the particles contained in solution are doped with fluorescent dyes, and these dyes are then excited by light of a particular wavelength. The excitation light coming from a laser is coupled into the module via a flange joint for an optical waveguide. In the FCS module known from prior art, it is difficult to align the FCS detection volume with the sample area, which is to be investigated.